Questions And Answers

Some of our ESD benches have the wrist strap going directly to ground and others to a work bench ESD mat which (on the opposite corner) then goes through a resistor to ground. Which is right? - James, Dallas, TX

Answer

Neither are necessarily correct because of the dependency on the relationship of the wrist strap that is directly grounded and the potential of the workbenchmat. The concept of grounding at an ESD safe bench is to bring to the same potential all conductors, thus minimizing the possibility of a potential difference between two conductors or its resultant discharge. Power ground or earth ground happen to be a convenient potential to connect into because it is consistent within the controlled environment. If both the wrist strap and the ESD mat are connected to the same point at ground, then they have the same potential and are properly setup. The wrist strap that connects first to the ESD mat, second through the mat, third from the opposite corner of the mat and fourth to ground has the addition of the serial impedance of the mat (resistance and capacitance) to ground to contend with. At times the operator may be at a different potential than grounded bench equipment or ESD sensitive devices on the mat.